The invention relates generally to brush cards for electric motors and electric generators.
Electric motors generally consist of an axle holding an armature and commutator which are mounted in a housing. The housing contains a pair of field magnets (or electro magnetic windings, depending on the type of motor) which surround the armature. Electric current is supplied to the commutator by a pair of graphite/copper brushes. The brushes are generally mounted to the housing on a brush card. The brush card generally consists of a flat card die-stamped out of a paper based high pressure laminate, plastic or polyester glass sheet. In a majority of brush cards, the brushes are each carried in a hollow metal tube which houses both a brush and a biasing spring. The spring biases the brush towards the commutator ensuring the brush makes electrical contact with the commutator. The metal tube, which is often referred to as a brush tube, can be made of brass or steel, depending on the desired durability and reliability of the brush card assembly. The brush tubes are generally rectangular tubes having an open bottom, an open end and four legs projecting from the bottom. The brush tubes are attached to the card by passing the legs of the tubes through holes punched in the brush card and then crimping the portions of the legs which extend pass the brush card. The spring and the brushes are then inserted into the brush tubes.
While the use of brush tubes has proven to be a reliable method of mounting the brushes to the brush card, there are several disadvantages with this construction. Firstly, the added costs associated with mounting the brush tubes to the brush cards are not inconsequential. If the brush tubes are made of brass, the brush tubes alone will add several cents to the material costs of assembling the brush card. Furthermore, the steps of mounting the brush tubes to the card and then inserting the spring and brush into the brush tube add to the cost of manufacturing the brush card. In addition to added cost, the brush tubes also adds a point of failure to the finished brush card assembly, increasing the possibility that the electric motor will fail due to a poorly assembled brush card tube. Furthermore, the brush tubes, being made of metal, have a tendency to conduct heat and, during the course of extended operations, may become overheated. The overheated brush tubes may cause warping of the housing or surrounding brush card, causing the brushes to jam. Also, the continual heating and cooling of the brush tubes can cause the tubes to become loose, resulting in a motor that fails to meet the required decibel specifications. An improved brush card which is easier and less expensive to construct and which does not suffer from the drawbacks of existing brush cards is therefore desirable.
In accordance with the present invention, there is provided a brush card consisting of a non conductive sheet material having a commutator aperture, and a pair of tongue and groove connector elements. Each tongue and groove connector element consisting of at least one pair of parallel channels formed on the card adjacent the aperture and extending along the card perpendicular to the commutator aperture, the card forming a pair of parallel opposing channel edges adjacent the parallel channels. A portion of the card forms an elongated tongue separating each pair of channels, the tongue having a distal end extending towards the commutator aperture and a proximal end opposite the distal end. The brush card also includes a conductive brush slidingly mounted to each tongue, each brush having opposite first and second sides and a central groove dimensioned to receive the tongue. Each brush also has a first groove extending along the first side of the brush, the first groove dimensioned to receive one of the channel edges. Each brush also has a second groove extending along the second side of the brush, the second groove dimensioned to receive the other channel edge. The card further includes a biasing spring located on each tongue and positioned between the brush and the proximal end of the tongue, the biasing spring biasing the brush towards the commutator aperture.
With the foregoing in view, and other advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, the invention is herein described by reference to the accompanying drawings forming a part hereof, which includes a description of the preferred typical embodiment of the principles of the present invention.